Colorectal cancer (CRC) is one of the leading causes of world cancer deaths. To improve the survival rate of CRC, diagnosis and post-operative monitoring is necessary. Currently, biomarkers are used for CRC diagnosis and prognosis. However, these biomarkers have limitations of specificity and sensitivity. Levels of plasma lysyl-tRNA synthetase (KARS1), which was reported to be secreted from colon cancer cells by stimuli, along with other secreted aminoacyl-tRNA synthetases (ARSs), were analyzed in CRC and compared with the currently used biomarkers. The KARS1 levels of CRC patients (n = 164) plasma were shown to be higher than those of healthy volunteers (n = 32). The diagnostic values of plasma KARS1 were also evaluated by receiving operating characteristic (ROC) curve. Compared with other biomarkers and ARSs, KARS1 showed the best diagnostic value for CRC. The cancer specificity and burden correlation of plasma KARS1 level were validated using azoxymethane (AOM)/dextran sodium sulfate (DSS) model, and paired pre- and post-surgery CRC patient plasma. In the AOM/DSS model, the plasma level of KARS1 showed high correlation with number of polyps, but not for inflammation. Using paired pre- and post-surgery CRC plasma samples (n = 60), the plasma level of KARS1 was significantly decreased in post-surgery samples. Based on these evidence, KARS1, a surrogate biomarker reflecting CRC burden, can be used as a novel diagnostic and post-operative monitoring biomarker for CRC.

Recent development of the chemical inhibitors specific to oncogenic KRAS (Kirsten Rat Sarcoma 2 Viral Oncogene Homolog) mutants revives much interest to control KRAS-driven cancers. Here, we report that AIMP2-DX2, a variant of the tumor suppressor AIMP2 (aminoacyl-tRNA synthetase-interacting multi-functional protein 2), acts as a cancer-specific regulator of KRAS stability, augmenting KRAS-driven tumorigenesis. AIMP2-DX2 specifically binds to the hypervariable region and G-domain of KRAS in the cytosol prior to farnesylation. Then, AIMP2-DX2 competitively blocks the access of Smurf2 (SMAD Ubiquitination Regulatory Factor 2) to KRAS, thus preventing ubiquitin-mediated degradation. Moreover, AIMP2-DX2 levels are positively correlated with KRAS levels in colon and lung cancer cell lines and tissues. We also identified a small molecule that specifically bound to the KRAS-binding region of AIMP2-DX2 and inhibited the interaction between these two factors. Treatment with this compound reduces the cellular levels of KRAS, leading to the suppression of KRAS-dependent cancer cell growth in vitro and in vivo. These results suggest the interface of AIMP2-DX2 and KRAS as a route to control KRAS-driven cancers.

Background and aims

Targeting costimulatory receptors with agonistic antibodies is a promising cancer immunotherapy option. We aimed to investigate costimulatory receptor expression, particularly 4-1BB (CD137 or tumor necrosis factor receptor superfamily member 9), on tumor-infiltrating CD8⁺ T cells (CD8⁺ tumor-infiltrating lymphocytes [TILs]) and its association with distinct T-cell activation features among exhausted CD8⁺ TILs in hepatocellular carcinoma (HCC).

Approach and results

Tumor tissues, adjacent nontumor tissues, and peripheral blood were collected from HCC patients undergoing surgical resection (n = 79). Lymphocytes were isolated and used for multicolor flow cytometry, RNA-sequencing, and in vitro functional restoration assays. Among the examined costimulatory receptors, 4-1BB was most prominently expressed on CD8⁺ TILs. 4-1BB expression was almost exclusively detected on CD8⁺ T cells in the tumor-especially on programmed death 1 (PD-1)^high cells and not PD-1^int and PD-1^neg cells. Compared to PD-1^int and 4-1BB^neg PD-1^high CD8⁺ TILs, 4-1BB^pos PD-1^high CD8⁺ TILs exhibited higher levels of tumor reactivity and T-cell activation markers and significant enrichment for T-cell activation gene signatures. Per-patient analysis revealed positive correlations between percentages of 4-1BB^pos cells among CD8⁺ TILs and levels of parameters of tumor reactivity and T-cell activation. Among highly exhausted PD-1^high CD8⁺ TILs, 4-1BB^pos cells harbored higher proportions of cells with proliferative and reinvigoration potential. Our 4-1BB-related gene signature predicted survival outcomes of HCC patients in the The Cancer Genome Atlas cohort. 4-1BB agonistic antibodies enhanced the function of CD8⁺ TILs and further enhanced the anti-PD-1-mediated reinvigoration of CD8⁺ TILs, especially in cases showing high levels of T-cell activation.

Conclusion

4-1BB expression on CD8⁺ TILs represents a distinct activation state among highly exhausted CD8⁺ T cells in HCC. 4-1BB costimulation with agonistic antibodies may be a promising strategy for treating HCCs exhibiting prominent T-cell activation.